This invention relates to a detection arrangement for detection of signal variations in a signal comprising a signal processing device for processing the signal into a reference signal and a comparison circuit having a first input for the supply of the signal and a second input for the supply of the reference signal, an output of the comparison circuit assuming a first state if the signal has a smaller signal value than the reference signal and a second state if the signal has a larger signal value than the reference signal, while the signal processing device comprises a threshold circuit having a variable threshold value and an input for the supply of the signal, which threshold value depends upon the signal value of the signal, an output of this threshold circuit being coupled to an input of a signal hold circuit for holding the variable threshold value forming the reference signal, while, when the variable threshold value is passed with a difference value by the signal in a first and a second direction, respectively, the variable threshold value follows the signal with a lag proportional to the difference value, characterized in the threshold circuit comprises adjusting means for adjusting the difference value.
Such a detection arrangement can generally be used, for example, to detect signals disturbed by noise, such as, for example, pulsatory signals.
A detection device is known from U.S. Pat. No. 3,708,678, in which FIG. 1 shows a comparison circuit (A2), in which a signal is supplied to a first input (-) and the signal is supplied to a second input (+) via to antiparallel connected diodes and a capacitor. The signal processing circuit is therefore constituted by the diodes and the capacitor. Peaks and valleys of a signal supplied to the detection circuit can be followed, except for a difference value, such as, for example, a diode threshold voltage of a forward biased diode, even if the signal is disturbed by noise. As is described in column 4 on lines 3-10, larger difference values than one diode threshold voltage also may be attained by arranging diodes in series in the antiparallel combination. If a different number of diodes are arranged per branch in the antiparallel combination, then unequal difference values are obtained for the two signal directions. The known detection device includes means for adjusting the signal source, but does not disclose means for adjusting the difference value (i.e. the diode voltage) within the detection device. A disadvantage of the detection device described in the aforementioned U.S. Patent is that the detection device cannot be adapted to different signal-to-noise conditions, as a result of which the device cannot operate satisfactorily in unfavourable signal-to-noise conditions and/or at comparatively small signals.